1. Field of the Invention
The present invention relates to a swash plate-type, variable displacement compressor for use in vehicular air conditioning apparatus. More particularly, this invention relates to a swash plate-type, variable displacement compressor that maintains piston top clearance at substantially zero over a whole range of oblique angles of swash plate.
2. Description of Related Art
In FIG. 1, a known swash plate-type, variable displacement compressor 100 used in vehicular air conditioning apparatus is shown. A cashing of the compressor 100 includes a front housing 102, a cylinder block 101 and a cylinder head 103. A drive shaft 106 is provided which passes through the center of front housing 102 and cylinder block 101. Drive shaft 106 is rotatably supported by front housing 102 and cylinder block 101 via bearings 107a and 107b. In cylinder block 101, a plurality of cylinder bores 108 are provided equiangularly around an axis XO of drive shaft 106. In each of cylinder bores 108, a piston 109 is slidably disposed. Pistons 109 are capable of reciprocation along axes parallel to the axis X0.
A rotor 110 is fixed to drive shaft 106, so that rotor 110 and drive shaft 106 may rotate together. Rotor 110 has an arm 117, and a hole 117a having an axis oblique to the axis X0 is provided in a terminal portion of arm 117. Front housing 102 and cylinder block 101 cooperatively define a crank chamber 105. Within crank chamber 105, a swash plate 111 having a penetration hole 120 at its center portion is accommodated, and drive shaft 106 penetrates through swash plate 111. Penetration hole 120 of swash plate 111 has a complex shape so as to enable changes in the oblique angle of swash plate 111 with respect to the axis X0. A bracket 115 is provided on the front housing-side surface of swash plate 111, and a guide pin 116 is fixed to a terminal portion of bracket 115. A spherical part 116a provided on the top of guide pin 116 is slidably fitted into hole 117a. Because spherical part 116a moves within hole 117a, the oblique angle of swash plate 111 may vary with respect to the axis XO. Hereafter, this connection mechanism including arm 117 of rotor 110, hole 117a, and guide pin 116, is labeled K. The circumferential portion of swash plate 111 has a shape of plane ring and is connected slidably to tail portions of pistons 109 via pairs of shoes 114.
When drive shaft 106 is driven by an external power source (not shown), rotor 110 also rotates around the axis XO together with drive shaft 106. Swash plate 111 also is made to rotate by rotor 110 via connection mechanism K. Simultaneously with the rotation of swash plate 111, the circumferential portion of swash plate 111 exhibits a wobbling motion. Only a component of the movement of the wobbling, circumferential portion of swash plate 111 in the axial direction parallel to the axis XO is transferred to pistons 109 via sliding shoes 114. As a result, pistons 109 are made to reciprocate within cylinder bores 108. Finally, in the operation of a refrigeration circuit, the refrigerant may be introduced repeatedly from an external refrigeration circuit (not shown) into a compression chamber, which is defined by the piston top of piston 109, cylinder bore 108, and valve plate 104, via suction chamber 130. The refrigerant then may be compressed by reciprocating piston 109, and the refrigerant subsequently may be discharged to the external refrigeration circuit via discharge chamber 131.
However, known compressors, such as that shown in FIG. 1, may exhibit several deficiencies. First, there may be a problem of controlling piston top clearance. Second, in such known compressors, because the frictional resistance against the inclining movement of swash plate 111 is large, changes in the oblique angel of the swash plate are not smooth. Third, there may be a problem with vibration of the compressor.
With reference to FIG. 1, the center of changes in the oblique angle of swash plate 111 is located at point Z. When the oblique angle of swash plate 111 changes, a resistant force is created due to frictional contact of spherical part 116a and the inner surface of hole 117a. The distance between the contact point of spherical part 116a and the inner surface of hole 117a and the center of changes in the oblique angle of the swash plate is relatively large. As a result, the resistant force due to the frictional contact of spherical part 116a and hole 117a impedes smooth changes to the oblique angle of swash plate 111.
With further reference to FIG. 1, the swash plate may be designed so as to have a center of gravity located on the axis XO when the oblique angle of the swash plate is minimized. The center of gravity of the swash plate deviates from the axis XO as the oblique angle of the swash plate increases. As the oblique angle of the swash plate increases, the distance between the center of gravity of the swash plate and the axis increase monotonically. Thus, as the oblique angle of the swash plate increases, the degree of unbalance due to the shift in the center of gravity of the swash plate also increases monotonically. As a result, a vibration of the whole compressor occurs during operation due to that unbalance.
A need has arisen to provide a swash plate-type, variable displacement compressor having a connection mechanism between the rotor and the swash plate that keeps the piston top clearance substantially zero over a whole range of oblique angles of the swash plate. It is a technical advantage of the present invention that the compressor may maintain the dead volume at substantially zero by keeping the piston top clearance at about zero over the range of oblique angles of the swash plate. Thus, the volumetric efficiency of the compressor is improved. A further need has arisen to provide a connection mechanism between the rotor and the swash plate, such that the impeding, frictional force acting against the inclining movement of the swash plate is suppressed. It is a further technical advantage of the compressor that the inclining movement of the swash plate becomes smooth, and the responsiveness of the compressor to changes in demanded capacity improves. An additional need has arisen to provide a swash plate, the center of gravity of which shifts less from the axis of the drive shaft than that of known compressors, when the oblique angle of the swash plate is changed. It is an additional technical advantage of such compressors that the vibration of the whole compressor due to an unbalanced center of gravity of the swash plate with regard to the axis of the drive shaft, may be reduced.
In an embodiment of the invention, a swash plate-type, variable displacement compressor comprises a front housing, a cylinder block, and a cylinder head. A drive shaft is supported rotatably by the front housing, and the cylinder block. A rotor is fixed to the drive shaft so as to be rotatable with the drive shaft. A plurality of pistons are accommodated slidably in a corresponding plurality of cylinder bores which are provided and arranged through an end surface of the cylinder block, and axes of the cylinder bores are arranged about a virtual cylinder having a radius R and formed around an axis X of the drive shaft. A central portion the drive shaft penetrates through a swash plate, and each of the pistons is connected to the swash plate via a pair of shoes. A connection mechanism is operably connected between the rotor and the swash plate, and the connection mechanism enables the swash plate to change its oblique angle with respect to the axis X of the drive shaft. The swash plate comprises a flat ring and a second ring, and the pistons are connected to the flat ring from inside. The connection mechanism further comprises a first arm and a second arm provided on the rotor, a pin, and a third arm formed on the swash plate. The pin extends in a direction tangential to the surface of the virtual cylinder.
Other objects, features, and advantages of this invention will be understood from the following description of preferred embodiments with reference to the accompanying drawings.